The present invention relates to a micromachine switch used in a milliwave circuit and microwave circuit.
Switch devices such as a PIN diode switch, HEMT switch, micromachine switch, and the like are used in a milliwave circuit and microwave circuit. Of these switches, the micromachine switch is characterized in that the loss is smaller than that of the other devices, and a compact high-integrated switch can be easily realized.
As a conventional micromachine switch, for example, a switch is described in Japanese Patent Laid-Open No. 9-17300 (U.S. Pat. No. 5,578,976). FIG. 13 is a plan view showing the structure of this micromachine switch. FIG. 14 is a sectional view taken along the line XIV-XIVxe2x80x2 of the micromachine switch shown in FIG. 13.
As shown in FIGS. 13 and 14, signal lines 102a and 102b, lower electrode 111, post 112, and control lines 116a and 116b are formed on a dielectric substrate 104. A GND plate 105 is formed on the lower surface of the dielectric substrate 104.
The signal lines 102a and 102b are disposed apart from each other at a gap G. The signal lines 102a and 102b are lines for flowing high-frequency electromagnetic energy.
The lower electrode 111 is formed apart from the signal lines 102 and 102b including the gap G. The lower electrode 111 has a rectangular shape as a whole.
The control lines 116a and 116b are connected to side surfaces of the lower electrode 111 on the signal line 102a side and on the signal line 102b side, respectively. The control lines 116a and 116b are parallel to the signal lines 102a and 102b, respectively. A voltage for controlling the operation of a micromachine switch 101 is selectively applied from the control lines 116a and 116b to the lower electrode 111.
The post 112a is formed apart from the lower electrode 111 on an extension line from the gap G to the lower electrode 111.
The base portion of an arm 113 is fixed on the upper surface of the post 112. The arm 113 extends from the upper surface of the post 112 to a portion above the gap G via a portion above the lower electrode 111. The arm 113 is made of an insulating member.
An upper electrode 114 is formed on the upper surface of the arm 113. The upper electrode 114 extends from a portion above the post 112 to a portion above the lower electrode 111. A capacitor structure is formed by the upper electrode 114 and lower electrode 111.
A contact 115 is formed on the distal end portion of the lower surface of the arm 113. The contact 115 extends from a portion above an end portion of the signal line 102a to a portion above an end portion of the signal line 102b via the gap G.
When no voltage is applied to the lower electrode 111, the contact 115 and signal lines 102a and 102b are apart from each other. Accordingly, a little high-frequency electromagnetic energy is transmitted from the signal line 102a to the signal line 102b. 
On the other hand, when a voltage is applied to the lower electrode 111, an electrostatic force for attracting the upper electrode 114 to the lower electrode 111 is generated. This force makes the arm 113 curve, and the contact 115 is displaced downward. When the contact 115 is brought into contact with the signal lines 102a and 102b, the high-frequency electromagnetic energy is transmitted from the signal line 102a to the signal line 102b. 
When the control lines 116a and 116b are disposed on the same side as that of the signal lines 102a and 102b, respectively, the high-frequency electromagnetic energy flowing in the signal lines 102a and 102b leaks out into the control lines 116a and 116b. That is, the conventional micromachine switch 101 has a large energy loss. An increase in frequency of the energy makes this problem conspicuous.
When the distance between the signal lines 102a and 102b and the control lines 116a and 116b increases, the coupling amount of high-frequency electromagnetic energy becomes small. To reduce the energy loss, therefore, the lower electrode 111 continuous with the control lines 116a and 116b may be apart from the signal lines 102a and 102b. 
However, the distance between the lower electrode 111 and signal lines 102a and 102b cannot be made large by the following reasons.
First, a decrease in length of a portion of the arm 113 placed above a space from the upper portion of the post 112 to the lower electrode 111 requires a large voltage to drive the micromachine switch 101. Therefore, to drive the micromachine switch 101 using a low voltage of 40V or less, a distance between the post 112 and lower electrode 111 need be made long.
In addition, if the length of the portion of the arm 113 from the upper electrode 114 to the contact 115 becomes long, the weight of the contact 115 makes the arm 113 curve. Thus, since a distance between the upper electrode 114 and contact 115 cannot be set long, the distance between the lower electrode 111 and the signal lines 102a and 102b must be inevitably shortened.
The present invention has been made to solve the above problem, and has as its object to reduce the loss of energy flowing in the signal line opened/closed by the micromachine switch.
In order to achieve the above object, a micromachine switch of the present invention is characterized by comprising at least two signal lines disposed apart from each other at a gap on a substrate and each having a fixed contact, a movable contact arranged above the fixed contacts via the gap and attached to an arm to connect the signal lines to each other in a high-frequency manner by the operation of the arm, an electrode disposed apart from the gap and each of the signal lines to receive a control signal to drive the arm, and a control line for connecting the control signal from a control terminal to the electrode, wherein the control line and the control terminal are disposed farther away from each of the signal lines than a position of the electrode.
In this case, in one structure of the control line, the portion of the control line, which is connected to the electrode, is formed obliquely with respect to one of the signal lines disposed on the same side as that of the control line. Alternatively, the control line is so formed as to extend from the electrode as a start point in a direction apart from one of the signal lines disposed on the same side as that of the control line.
In another structure, the control line includes a parallel portion which has one end connected to the electrode and is formed parallel to one of the signal lines disposed on the same side as that of the control line, and an inclined portion formed obliquely with respect to the one of the signal lines disposed on the same side as that of the control line, and connected to the other end of the parallel portion. Alternatively, the control line includes a parallel portion which has one end connected to the electrode and is formed parallel to one of the signal lines disposed on the same side as that of the control line, and an inclined portion connected to the other end of the parallel portion and extending from the other end of the parallel portion as a start point in a direction apart from the one of the signal lines disposed on the same side as that of the control line.
In this case, a length of the parallel portion of the control line is preferably not more than a xe2x85x9 wavelength of a high-frequency signal flowing the signal lines.
In still another structure, the control line is connected to one of side surfaces of the electrode, which opposes the gap.
By forming the control line as described above, as a whole, the distance between the signal line and control line becomes larger than that in a case in which the control line is formed to be parallel to the signal line. In addition, when the control line having a predetermined length is to be formed, the component of the control line parallel to the signal line is shortened. An increase in distance between the signal line and control line and a decrease in component of the control line parallel to the signal line reduce the coupling amount from the control line to the signal line, thereby reducing the loss of energy flowing in the signal line.
On the other hand, in a structure, the electrode is a lower electrode disposed on the substrate apart from the gap and the signal lines.
In another structure, the electrode is an upper electrode disposed on the arm apart from the signal lines.
In still another structure, the electrode is a lower electrode disposed on the substrate to be apart from the gap and the signal lines, and an upper electrode disposed on the arm to be apart from the signal lines.
In all structures of the electrode, the effect described above can be obtained.
In the micromachine switch described above, when the control line is connected to one of the side surfaces of the electrode, which opposes the gap, the electrode may include a lower electrode disposed on the substrate to be apart from the gap and the signal lines, the switch may further comprise a post disposed apart from the lower electrode to support the arm, and the control line may be so formed as to pass between the lower electrode and the post. This can shorten the length of the control line when the plurality of micromachine switches are controlled through one control line.
When the switch includes the upper electrode as an electrode, the arm may include an insulating member to insulate and separate the upper electrode from the movable contact. This can reduce the coupling between the signal line and control line.
In a structure, the substrate is a dielectric substrate.
In another structure, the substrate is a semiconductor substrate.
The switch may further comprise a post for supporting the arm, and the electrode may include a lower electrode disposed on the substrate and sandwiched between the gap and post.
The switch may further comprise a post for supporting the arm, and the electrode may include a lower electrode disposed on the substrate on the different side from the post via the gap.